Self steering rail vehicle

ABSTRACT

A rail vehicle which has at least first and second wheelsets ( 12, 14 ) and wherein the treads ( 34 ) of the wheels are coned at an angle of between 4 DEG and 9 DEG, each wheelset ( 12, 14 ) is engaged with axle boxes, each axle box has an inclined chevron-type primary suspension ( 44 A- 44 D), and no linkage connects the first wheelset ( 12 ) to the second wheelset ( 14 ).

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to a self steering rail vehicleand more particularly is concerned with a self steering railway bogie.

[0002] It is highly desirable for a wheel set of a rail vehicle to beable to travel over straight (tangent) and curved track without contactor with minimal contact between flanges of the wheels and sides of therails. By reducing or eliminating this type of contact rail and wheelwear are reduced and vehicle stability is enhanced.

[0003] Self steering bogies of which the applicant is aware make use ofa sandwich-type primary suspension with an interconnecting linkagebetween wheelsets. It is however highly advantageous if it is possibleto eliminate the linkage because space in the bogie, which such alinkage occupies, can readily be utilised for brake gear and otherimportant structural components such as the bolster or main loadcarrying components of the bogie. The linkage requires an accuratelymanufactured sub-frame which is fairly substantial in mass and which isexpensive. It follows therefore that without the linkage the unsprungmass of the vehicle or bogie is reduced considerably and this implies areduction in the dynamic forces which act between the wheels and rails.Ancillary components are simplified and the overall mass compares veryfavourably with a conventional bogie of the same type eg. a three piecefreight bogie with a bolster and two side frames encompassing twowheelsets, a secondary suspension (rubber or steel springs) and brakegear.

SUMMARY OF INVENTION

[0004] The invention provides a rail vehicle which has at least firstand second wheelsets and wherein:

[0005] (a) the treads of the wheels are coned at an angle of between 4°and 9°,

[0006] (b) each wheelset is engaged with axle boxes,

[0007] (c) each axle box has an inclined chevron-type primarysuspension, and

[0008] (d) no linkage connects the first wheelset to the secondwheelset.

[0009] The wheel treads may be coned at an angle of from 5° to 8° butpreferably are coned at an angle less than 7°. The cone angle is chosento allow the wheelsets to self-steer around the sharpest curves on arail track without material contact of the flanges of the wheels withthe rails. With a higher or steeper cone angle the likelihood of flangecontact is reduced but the critical speed at which instability can occuris also reduced.

[0010] The primary suspension may be of any appropriate type butpreferably is of the type described in the specification of SouthAfrican patent No. ZA97/4198 or ZA89/3711.

[0011] The rail vehicle may include an elongate underframe or chassiswith the first and second wheelsets being located respectively towardsopposed ends of the underframe or chassis.

[0012] On the other hand in a different form of the invention the railvehicle includes at least one bogie and the first and second wheelsetsform part of the bogie. With this form of the invention the rail vehiclewill normally include at least two bogies at spaced positions to supportan underframe or chassis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is further described by way of example withreference to the accompanying drawings in which:

[0014]FIG. 1 is a perspective view of a self steering bogie according tothe invention wherein brake gear and certain ancillary equipmentassociated with the bogie have been omitted for clarity of illustration,

[0015]FIG. 2 is schematic end view of portion of a wheel used in thebogie of FIG. 1, and

[0016]FIG. 3 illustrates in plan two wheelsets of a rail vehicle with alonger wheel base than the bogie of FIG. 1, with preferred suspensionassemblies, and

[0017]FIG. 4 is a side view of a suspension arrangement used in thebogie of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

[0018]FIG. 1 of the accompanying drawings illustrates in perspective aself steering bogie according to the invention. As has been indicatedbrake gear and other ancillary equipment associated with the bogie havebeen omitted for clarity of illustration. Such gear and equipment playno role in an understanding of the invention.

[0019] The bogie 10 includes first and second wheelsets 12 and 14respectively which are mounted in side frame members 16 and 18. A crossmember 20 extends between the frame members 16 and 18 and, in use, ispivotally connected at a central point 22 to a chassis of a rail vehicle(not shown). Springs 24 or similar suspension elements support the crossmember on the frame members. The springs 24 are preferably made fromrubber laminations and may be circular cylindrical in shape. It has beenfound that rubber springs are highly suitable for they can functionunder overload conditions while retaining self-damping characteristics.The self-damping characteristics, in turn, eliminate friction wedges orsimilar devices which are used to provide a measure of friction dampingwhen suspension elements, other than rubber springs, are used.

[0020] Each wheelset 12, 14 includes an axle 26 and wheels 28. Thewheels roll on rails 30.

[0021]FIG. 2 is an end view of a portion of an axle 26 and a wheel 28.The wheel has a flange 32 and a track-engaging portion or tread 34. Thetread portion is coned in the sense that it presents a conical surface,ie. a surface which is inclined to a line 36 which is parallel to theaxle 26. In accordance with a preferred feature of the invention thewheel tread is coned at an angle 38 which lies in the range of from 4°to 9°, typically in the range of from 5° to 7°. The cone angle is chosento limit flange contact with the rail, taking into account the maximumrail curvature. The wheel tread has a width 40 which should be as wideas possible and the flange 32 is relatively thin to ensure maximum treadcontact with the top of an associated rail 30. It is pointed out thatthe wheel flange 32 should only contact a side of the rail 30 underunusual conditions eg. very poor track and or very sharp radius curves.In other words the wheel flange is a safety feature which comes intoplay under extreme conditions.

[0022]FIG. 3 depicts in plan the wheelsets 12 and 14 of a relativelylong vehicle, on the rails 30. Each axle 26 is mounted to axle boxeswhich have a primary suspension consisting of inclined elastromericchevron-type suspensions designated 44A, 44B, 44C and 44D respectively,in the manner described in the specification of South African patent No.97/4198 or 89/3711. The disclosures in these specifications are to bedeemed to be incorporated in this specification.

[0023] The inclined chevron-type primary suspensions referred to actlike springs and provide a very low yaw restraint, some verticaldeflection under load and a high lateral spring rate to ensure stabilityand a high critical speed for “hunting” ie. the yaw oscillation of therail vehicle about its own centre of gravity.

[0024]FIG. 4 is a side view of the chevron-type suspensions 44 referredto in connection with FIG. 3. The chevrons on the left side of thedrawing are illustrated partly sectioned, to show their construction.The axle 26 extends through an axle box 50 and is mounted on bearingswhich are located in the axle box. The axle is directly connected to apair of wheels 28.

[0025] The axle box has two inclined support surfaces 52 and 54respectively each of which has an upstanding respective spigot 56 forcorrectly positioning the axle box with respect to chevrons 58 and 60,on opposed sides of the axle box. Other means of locating the chevronscorrectly could be used in place of the spigots.

[0026] Each of the chevrons 58 and 60 includes angled members, in thiscase steel plates 62, which are bonded to intermediate elements 64 ofrubber or an equivalent elastomeric material.

[0027] The lowermost plate of each chevron, designated 66, has abridging plate 68 in which is formed a hole, not shown, and thecorresponding spigot 56 is engaged with the hole when the chevron isplaced on the inclined surface 52 or 54 of the axle box. The plate 66 isessentially parallel to the plates 62.

[0028] An upper plate 70 is fixed to the body of the rail vehicle. Stops72 or similar devices locate the upper plates 58 and 60 correctly.

[0029] Viewed in plan the chevrons 58 and 60 are inclined to thelongitudinal axis of the axle and, viewed from the side, the chevronsare inclined to the vertical.

[0030] The aforementioned type of suspension locates the wheel setcorrectly and keeps the wheel set geometry in a desired configuration.

[0031] No linkages extend between the wheel sets. The linkages areomitted and this step can be taken since stability in yaw is achieved byselecting the correct chevron angle and hence the most suitable lateralspring rate.

[0032]FIG. 3 illustrates the concept of focalising. This concept isfully described in the specification of patent No. ZA97/4198. In thebogie of the invention if the wheel base is relatively short incomparison with the track gauge and minimum curvature then focalising isnot usually required. On the other hand if the wheel base is relativelylarge compared to the track gauge and the curves are sharp thenfocalising would normally be required. Focalising can however readily beincorporated when chevrons with a small chevron angle are required.These chevrons can increase the yaw restraint substantially in sharpcurves unless they are focalised.

[0033] In other words with a bogie of the type shown in FIG. 1 it wouldnot normally be necessary to focalise the suspensions. On the other handif a first wheelset is positioned at one end of an elongate chassis anda second wheelset is positioned at an opposing end of the chassis itwill normally be appropriate to focalise the chevrons.

[0034] It has been found that by utilising the principles describedherein ie. by coning the wheel treads at an angle of from 4° to 9°,depending on the rail conditions, and by making use of inclinedelastromeric chevron-type primary suspensions that the requirement for alinkage, to achieve a self-steering capability, is dispensed with. Inoperation of the bogie of the invention each wheelset follows its ownpath when travelling on straight (tangent) or curved track. This ensuresthat the coned wheel treads roll on the track at all times through trackirregularities and curves with a very substantial reduction in rollingresistance. By way of contrast if the wheelsets are linked to each otherthey influence the motion of each other. They then tend to behave like aconventional rigid wheel base bogie.

[0035] With the self-steer bogie of the invention derailments arereduced because the coned wheels with low yaw restraint steer themselvesaway from a track irregularity. If a wheel flange 32 does contact therail 30 the point of contact is behind the centre of the vertical forceon the rail and this generates a vertical friction force downwardlywhich increases the adhesion of the wheel on the rail instead ofgenerating an unwanted vertical flange force ahead of the wheel whichcan lift that wheel over the rail and so result in a derailment.

[0036] Clearly it is preferred that the wheelsets of the bogie of theinvention are correctly aligned. Nonetheless a degree of misalignmentcan be tolerated as there is no interconnecting linkage between thewheelsets to generate incorrect tracking of one or both wheelsets.

[0037] The principles of the invention can be incorporated into a bogie,as is shown in FIG. 1, wherein two of the bogies are attached at spacedpositions to an underframe of a rail vehicle. Alternatively wheelsets ofthe kind used in the bogie are directly attached to an underframe of arail vehicle.

[0038] In designing the primary suspension for the bogie the springcharacteristics of the secondary suspension must be considered, togetherwith the leading dimensions of the bogie such as wheel diameter, trackgauge and wheel base, and the superstructure and load, includingparameters such as the bogie centre spacing, and the width and heightabove the rail. Empty and loaded vehicles have natural frequencies ofvibration about their principal axes and synchronous/critical conditionsarise when any one of these frequencies is the same as any of the inputfrequencies eg. hunting frequencies (lateral movement across the track)or frequencies induced by rail joints (in the longitudinal direction ofthe track) or the like. Coned wheels generate a sinusoidal motion acrossthe track depending upon cone angle, wheel diameter and track gauge witha wavelength which is very nearly constant. When the speed along thetrack and the wavelength of yaw oscillation of the wheelsets generate afrequency which is synchronous with any one of the natural frequenciesof the vehicle mass, then a critical condition is reached at which theoscillation cannot be damped and either the speed must be changed or aderailment will occur. This condition must be avoided by the correctdesign of the suspension of the bogies to suit the application to thewagon under which they will operate. It is preferable to have thecritical speeds higher than the maximum operating speed of the railvehicle. This is generally not difficult to achieve when properconsideration is given to all the parameters.

[0039] It is advisable to incorporate the lowest wheel tread conicityconsistent with the minimum radius of curve In order to have the longestwavelength sinusoidal hunting oscillation of each wheelset consistentwith the other parameters.

[0040] Under unusual conditions there may be a very low critical speedand the vehicle may be accelerated through this critical condition. Thisarrangement is however not recommended because operating conditionscould arise under which the critical speed is commonly encountered.

[0041] Since the wheels roll and do not slide on the rails the wheeltreads tend to harden resulting in very little wear. When wear doesoccur, usually from brake block action, then it is even and very little“hollow wear” is experienced.

[0042] The bogie of the invention is simple in design, effective inoperation, substantially maintenance free and easy to access shouldservice be required after unusual occurrences such as accidents orderailments. Expensive accurately made linkages are an undesirablefeature of self-steered and steered bogies and, as stated, such linkagesare avoided in the invention by making use of inclined chevron-typeprimary suspensions which provide lateral stability as well as reducinghigh frequency vibrations.

1. A rail vehicle which has at least first and second wheelsets, eachwheelset including an axle and wheels fixed to the axle, and wherein:(a) the treads of the wheels are coned at an angle of between 4° and 9°,(b) each axle is engaged with axle boxes, (c) each axle box haschevron-type primary suspensions which, in elevation, are inclined tothe vertical, and (d) no linkage connects the first wheelset to thesecond wheelset.
 2. A rail vehicle according to claim 1 wherein thewheel treads are coned at an angle of from 5° to 8°.
 3. A rail vehicleaccording to claim 1 or 2 which includes an elongate underframe with thefirst and second wheelsets being located respectively towards opposedends of the underframe.
 4. A rail vehicle according to claim 3 whereinthe suspensions are focalized.
 5. A rail vehicle according to claim 1 or2 wherein the first and second wheelsets form part of a bogie.
 6. A railvehicle according to claim 5 which includes at least two of the bogiesat spaced positions to support an underframe.